This invention relates generally to electrical control systems and more particularly to an electrical system for stopping the engine and removing power from all electrical control circuits of an aerial work platform due to the upper work platform or basket coming into dangerously close proximity to an overhead obstruction.
Systems responsive to obstructions for disabling various types of apparatus including aerial work platforms are generally known. Such apparatus typically includes some type of sensor which when it comes into contact with the obstruction, automatically disables the power circuit to the devices which move the platform. Such apparatus is disclosed, for example, in U.S. Pat. No. 3,670,849, entitled, "Aerial Personnel Platform With Proximity Sensing System", which issued to E. Milner, Jr. on June 20, 1972. There inflatable tubes operate to actuate an electrical switch to open the power circuit of a boom structure when the basket strikes an obstruction.
Overhead guards in combination with the platform are also known. Such devices are shown and described, for example, in U.S. Pat. No. 2,815,250, entitled, "Machine With Elevatable and Traveling Carriage", issued to W. E. Thornton-Trump on Dec. 3, 1957, and U.S. Pat. No. 3,638,758, entitled, "Overhead Guard", issued to A. Weisker on Feb. 1, 1972. In U.S. Pat. No. 2,815,250, there is disclosed a vertical element which projects over the top of the railing of the work platform and operates such that if the platform is raised too high so as to pin the operator between an overhead obstruction and the platform, the operator's body is pressed down on the vertical element to actuate means for moving the platform downward. In U.S. Pat. No. 3,638,758, an overhead guard is utilized in conjunction with a safety seat switch so that an operator must be seated when the overhead guard is in place over the operator to avoid the possibility of the operator contacting any overhead structure. The switch, however, is not actuated by the overhead guard.
Accordingly, it is an object of the present invention to provide an improvement in aerial work platforms.
It is another object of the invention to provide an electrical control circuit for disabling the work platform when the work platform comes in close proximity to an overhead obstruction.
It is yet another object of the invention to provide an electrical control circuit which operates in response to the sensing of an overhead obstruction to automatically disable the apparatus and thus remove the possibility of injury to an operator located on the upper work platform or control box thereof.
Still a further object of the invention is to disable the engine and remove power from the electrical control circuits of an aerial work platform in response to overhead impact sensing apparatus located on the upper work platform or control box striking or contacting an external object or obstruction.